Libya's deputy industry minister, Hassan al-Droui, was shot dead during a visit to his hometown of Sirte, east of Tripoli, security and hospital sources said.
The identity of the shooters was not immediately known, but the official's death was the first assassination of a member of the transitional government since the fall of Muammar Gaddafi's government in October 2011.
Droui was killed near Mekmdas market in central Sirte after evening prayers on Sunday, media coordinator for the Tripoli Security Directorate, Essam Naas, confirmed to local newspaper, Libya Herald.
"Hassan al-Droui, the deputy minister for industry, was killed by unknown attackers overnight, during a visit to his native city of Sirte," a security official told AFP news agency.
"Unidentified gunmen sprayed bullets on Mr Droui in central Sirte," the official said, speaking on condition of anonymity.
An official at the city's Ibn Sina hospital confirmed the deputy minister's death and added that he had suffered bullet wounds to several parts of his body.
Droui was a former member of the National Transitional Council, the political arm of the rebellion that brought an end to Gaddafi's 42-year rule.
He was appointed deputy minister for industry by the transitional government's first prime minister, Abdelrahim al-Kib, and kept his job when Ali Zeidan took over.
Droui's hometown, which lies on the Mediterranean coast about 400 kilometres east of the capital Tripoli, was the last government bastion to fall into rebel hands in 2011.
Since the collapse of Gaddafi's autocratic government, Libya has been plagued by sporadic violence, including a string of assassinations targeting top army and security officials.
Fighting between rival tribes in southern Libya killed 19 people on Saturday and wounded another 20, a local official said.
"Violent confrontations broke out between Toubous and Awled Sleiman early this morning," Ayoub al-Zarrouk, chief of the local council in Sebha told AFP.
"So far there are 19 dead and 20 wounded."
Local sources said the clashes were sparked by the death on Thursday of a militia chief linked to Awled Sleiman, adding that the tribe accused the Toubous of murdering him.
Saturday's fighting is the worst between the tribes since they struck a ceasefire agreement in March 2012 following deadly battles that killed at least 150 people and wounded 400 others.
The Toubous are black oasis farmers by tradition who also live in southern Libya, northern Chad and Niger.
They have complained in the past of attempted ethnic cleansing against their community by Arab tribesmen.